1. Field of the Invention
This invention generally relates to a driving apparatus for driving to move an object in a desired direction, and, in particular, to an X-Y drive apparatus for driving to move an X-Y table suitable for use in a system for automatically mounting various electronic components and the like on a circuit board.
2. Description of the Prior Art
An X-Y drive apparatus is well known in the art and such a typical prior art X-Y drive apparatus is illustrated in FIGS. 2 through 4. FIG. 2 shows in perspective view a typical prior art X-Y table drive apparatus including an X table drive unit 1 and a Y table drive unit 2. The X and Y table drive units 1 and 2 are identical in structure excepting the fact that they are placed one on top of another oriented perpendicular to each other. In this structure, the X table drive unit 1 is fixedly mounted on a base (not shown) and the Y table drive unit 2 is mounted on the X table drive unit 1 such that the Y table drive unit 2 may move in the X direction back and forth.
As shown in FIG. 4, each of the X and Y table drive units 1 and 2 includes a bed 3 having a generally U-shaped cross sectional shape, and a pair of side plates 4a and 4b is fixedly attached to the both sides of the bed 3 extending vertically upward. The bed 3 are elongated in shape horizontally, as are the side plates 4a and 4b. As shown in FIG. 3, a motor 5 and a connector 6 for the motor and sensors are fixedly mounted at one end of the bed 3 through a fixture member 7. A stationary bearing member 8 including a bearing 8' for rotatably supporting one end of a ball screw unit 10 is fixedly attached at the opposite end of the bed 3. The motor 5 is operatively coupled to the ball screw unit 10 through a coupling unit 9. The ball screw unit 10 includes a male screw 11, a female screw (not shown) of a nut 16 and a plurality of balls (not shown) interposed between them.
As shown in FIG. 3, the male screw 11 has one end rotatably supported by the stationary bearing member 8 through the bearing 8' and the opposite end of the male screw 11 has an integrally formed shaft section 11a which is rotatably supported by a stationary bearing 14 in a bearing unit 12. The movement of the shaft section 11a in the axial direction may be limited by eliminating the clearance in the stationary bearing 14 in the axial direction by tightening a bearing nut 13, and since the shaft section 11a is operatively coupled to the coupling unit 9, a rotationary force may be transmitted from the motor 5.
The nut 16 whose female screw is in engagement with the male screw 11 through balls (not shown) is fixedly attached to a table 17 having a generally T-shaped cross section as shown in FIG. 4. The table 17 is formed with a pair of projections 17a which project upwardly beyond the top end of the side plates 4a and 4b. These projections 17a serve to support thereon the Y table drive unit 2. A stopper 18 having a predetermined length is fixedly attached to one end surface of the table 17 so as to limit the movement of the table 17 in the axial direction. A pair of sliders 19, each having a generally inverted-U-shaped cross section, is fixedly attached to the bottom surface of the table 17 and these sliders 19 are slidably mounted on a pair of guide rails 15 which are mounted on respective mounting surfaces 3a of the bed.
The bed 3 is formed with a pair of sensor mounting grooves 20 in which sensors 51a and 51b are mounted for detecting the position of the table 17 relative to the rails 15. As shown in FIG. 3, a plurality of cover positioning grooves 22 are provided for positioning a top cover 21, and, as shown in FIG. 4, a plurality of cover positioning grooves 50 are provided for positioning the side plates or covers 4a and 4b.
In operation, upon power up, power is supplied from an external source through the connectors 6 of the respective X and Y table drive units 1 and 2 to the respective motors 5 and the various sensors 51a and 51b mounted in the sensor mounting grooves 20. When the power supply voltage is applied to the motor 5 of X table drive unit 1, the motor 5 is driven to rotate so that a rotating force is transmitted to the ball screw unit 10 through the coupling unit 9. Since the male screw 11 of the ball screw unit 10 rotates, the nut 16 and thus the table 17, to which the nut 16 is fixedly attached, moves longitudinally along the guide rails 15. Since the table 17' of Y table drive unit 2 may move in the Y direction independently from the X table drive unit 1, the table 17' of Y table drive unit 2 may be driven to move in any direction in a plane defined by the X and Y axes by controlling the operation of the motor 5 of each of the X and Y table drive units 1 and 2 via a control circuit (not shown).
However, in the above-described prior art X-Y drive unit, since the Y table drive unit 2 is mounted on the X table drive unit 1, a motor having a larger capacity must be used for the motor 5 of the X table drive unit 1, which is disadvantageous since the overall structure tends to become bulky and the speed of operation tends to be limited. In addition, in view of the added weight, the ball screw unit 10 must be carefully designed to have a sufficient rigidity and an optimal diameter. Moreover, since the motor 5 of Y table drive unit 2 executes a linear motion together with the Y table drive unit 2, a cord or line connected to the connector 6 also moves, so that a care must be exercised not to get such a cord or line tangled or cut during operation.